With reference to FIG. 12, an operation performed when a mobile station UE that establishes an RRC connection #1 in a cell #1 detects an RLF (Radio Link Failure), in a mobile communication system of the “LTE (Long Term Evolution)” scheme defined by the 3GPP, will be explained.
As illustrated in FIG. 12, in a state where the RRC connection #1 is established between the mobile station UE and the radio base station eNB#1, and an S1 connection #1 is established between the radio base station eNB#1 and a mobile switching center MME, when the mobile station UE detects the RLF (Radio Link Failure) in step S5001, the mobile station UE performs a cell selection process (Cell Selection) in step S5002.
In step S5003, the mobile station UE transmits an “RRC Connection Re-establishment Request” to a radio base station eNB#2 that manages a cell #2 selected in the cell selection process.
In step S5004, when the radio base station eNB#2 stores context information (UE context) of the mobile station UE corresponding to a “Physical Cell Identity”, a “C-RNTI”, and a “shortMAC-I” included in the received “RRC Connection Re-establishment Request”, then the radio base station eNB#2 transmits an “RRC Connection Re-establishment” to the mobile station UE in step S5005.
In step S5006, the mobile station UE transmits an “RRC Connection Re-establishment Complete” to the radio base station eNB#2.
In step S5007, the radio base station eNB#2 transmits an “S1 Path Switch” to the mobile switching center MME, and in step S5008, the mobile switching center MME transmits an “RRC Connection Reconfiguration” to the mobile station UE.
In step S5009, the mobile station UE transmits an “RRC Connection Reconfiguration Complete” to the radio base station eNB#2, and in step S5010, the mobile switching center MME transmits an “S1 Path Switch Ack” to the radio base station eNB#2.
This completes switching of the RRC connection #1 to the RRC connection #2 and switching of the S1 connection #1 to the S1 connection #2. In this case, the RRC connection #2 is an RRC connection established between the mobile station UE and the radio base station eNB#2, and the S1 connection #2 is an S1 connection established between the radio base station eNB#2 and the mobile switching center MME.
However, in such a mobile communication system, the mobile station UE is configured to perform handover only to the cell controlled by the radio base station eNB in which the context information of the mobile station UE (UE context) is stored.
Therefore, there is a problem that when the above-described radio base station eNB#2 does not store the context information of the mobile station UE, then the above-described “RRC Connection Re-establishment” is denied, and thus, the mobile station UE cannot establish the RRC connection #2 with the radio base station eNB#2 that manages the cell #2 selected in the cell selection process.
Therefore, the present invention is intended to overcome the above-described problem. An object of the present invention is to provide a mobile communication method and a radio base station enabling a connection re-establishment (re-connection) to a radio base station in which context information of a mobile station is not stored.